Question: Solve for $n$ : $20 + n = -1$
Subtract $20$ from both sides: $ \begin{eqnarray} \\ 20 + n &=& -1 \\ \\ {-20} && {-20} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{20 + n} &\hphantom{=}& \hphantom{-1} \\ n &=& -1 {- 20} \\ \end{eqnarray} $ Simplify. $ n = -21$